Nonmagnetic Particles Research Articles

Магнитные состояния в модели поверхностного димера

For the electrons of surface dimer formed by adsorbed particle and substrate atom effects of the intra- and interatomic Coulomb interactions are taken into account. Two cases are considered: adsorption of magnetic particle on nonmagnetic substrate and adsorption of nonmagnetic particle on magnetic substrate. Analytical expressions for the surface dimer magnetization are obtained for the regimes of weak and strong dimer – substrate coupling

Magnetophoretic Control of Diamagnetic Particles Inside an Evaporating Droplet.

The present study reports the magnetophoresis of diamagnetic particles in an evaporating ferrofluid droplet. Both solid and ring magnet arrangements are used to investigate the effect of magnetic field distribution. The distance of the magnet from the droplet is varied to study the effect of magnetic field strength. The magnetic field distribution is computed using COMSOL multiphysics software. Magnetometer measurements have been carried out to validate the simulation results. The motion of particles and the drying pattern of evaporating ferrofluid droplets are visualized using the confocal microscopy technique. Both bright-field and fluorescence imagings have been carried out to observe the differential deposition of the fluorescent particle (microparticle) and magnetic nanoparticles in the absence and presence of a magnetic field. The velocity of diamagnetic particles as a function of magnetic field distribution and strength has been studied using the micro-PIV technique. In the absence of the magnetic field, a ring-shaped deposition pattern is observed. The mixture of microparticles (diamagnetic) and nanoparticles (magnetic) is deposited between the outer and inner edges of the ring. The diamagnetic particles occupy the inner and outer edges of the ring. Magnetic particles travel toward the higher magnetic field zone and diamagnetic particles move toward the smaller magnetic field zone when a magnetic field is applied by a solid magnet placed over the droplet. This can be attributed to the negative magnetic force originating from the difference between the susceptibility of magnetic and nonmagnetic particles. The negative magnetic force on the microparticle increases as the magnetic field intensity increases, causing the microparticle to convect faster toward the contact line. The deposition behavior can be reversed or suppressed using a ring magnet in place of a solid magnet. In this case, the negative magnetic force is stronger at the contact line region of the droplet and decreases as it approaches the center region of the droplet. The deposition behavior of diamagnetic particle depends on the balance between the Marangoni force and the magnetophoretic force. Overall, the present study demonstrates the capability of the controlled deposition of diamagnetic polystyrene particles by suitable arrangement of the solid and ring magnet.

Translatory and rotatory motion of exchange-bias capped Janus particles controlled by dynamic magnetic field landscapes

Magnetic Janus particles (MJPs), fabricated by covering a non-magnetic spherical particle with a hemispherical magnetic in-plane exchange-bias layer system cap, display an onion magnetization state for comparably large diameters of a few microns. In this work, the motion characteristics of these MJPs will be investigated when they are steered by a magnetic field landscape over prototypical parallel-stripe domains, dynamically varied by superposed external magnetic field pulse sequences, in an aqueous medium. We demonstrate, that due to the engineered magnetization state in the hemispherical cap, a comparably fast, directed particle transport and particle rotation can be induced. Additionally, by modifying the frequency of the applied pulse sequence and the strengths of the individual field components, we observe a possible separation between a combined or an individual occurrence of these two types of motion. Our findings bear importance for lab-on-a-chip systems, where particle immobilization on a surface via analyte bridges shall be used for low concentration analyte detection and a particle rotation over a defined position of a substrate may dramatically increase the immobilization (and therefore analyte detection) probability.

Optimization of Airflow Field for Pneumatic Drum Magnetic Separator to Improve the Separation Efficiency

Traditional dry magnetic separation has poor separation efficiency for fine-grained materials, and combining airflow and a magnetic field may be one of the most effective means to improve it. Based on the pneumatic drum magnetic separator developed by our team, an improved pneumatic magnetic separator with a segmented flow field is proposed, which pushes materials to move along the separation surface. Analysis of flow field in the separation zone and the forces on particles show that the improved pneumatic magnetic separator makes it easier to collect fine magnetic particles, while nonmagnetic particles are more easily removed by airflow. Separation test results also show that the iron grade and the recovery of concentrate improved from 37.89% and 74.75% to 51.76% and 91.79%, respectively. The separation efficiency of the pneumatic drum magnetic separator has been remarkably improved by optimizing airflow field in the separation zone.

How to Control the Microfluidic Flow and Separate the Magnetic and Non-Magnetic Particles in the Runner of a Disc.

Biochips play an important role in both medical and food industry safety testing. Moreover, magnetic activated cell sorting is a well-established technology for biochip development. However, biochips need to be manufactured by precision instruments, resulting in the high cost of biochips. Therefore, this study used magnetic-activation and mechanics theories to create a novel disc that could manipulate the microfluidic flow, mixing, reaction, and separation on the runner of the disc. The goal of the research was to apply in the field of biomedical detection systems to reduce the cost of biochips and simplify the operation process. The simulation and experimental investigation showed that the pattern of the reaction chamber was stomach-shaped and the reservoir chamber was rectangular-shaped on the disc. The microfluid could be controlled to flow to the reaction chamber from the buffer and sample chamber when the disc spun at 175~200 rpm within three minutes. This was defined as the first setting mode. The microfluid could then be controlled to flow to the reservoir chamber from the reaction chamber when the disc spun at 225 rpm within five to ten minutes. This was defined as the second setting mode. This verified that the pattern design of the disc was optimized for control of the microfluid flow, mixing, reaction, and separation in the runner of the disc by different setting modes.

Mechanical design of a superconducting demonstrator for magnetic density separation

The focus of this paper is on the mechanical design of a NbTi-based demonstrator magnet for magnetic density separation (MDS) that is being constructed at the University of Twente. MDS is a new recycling technology that allows the separation of non-magnetic particles based on their mass density, using a vertical magnetic field gradient and a ferrofluid. The unique mechanical design challenge for this type of magnet is the desired minimization of the distance between a sim1 m2 planar array of cryogenic racetrack coils and the ambient-temperature ferrofluid bath. The optimization of the magnet geometry results in a distance between the coils and ferrofluid of 50 mm. This is made possible by opting for conduction-cooling, for the inclusion of room-temperature rods that pass through the cold mass to support the cryostat, and for the geometry of the cassette that reacts to the Lorentz force.

Overview of in-capillary enzymatic reactions using capillary electrophoresis.

This review summarizes the research that has recently been performed on in-capillary enzymatic reactions integrated with capillary electrophoresis. The manuscript is subdivided in homogeneous and heterogeneous approaches. The main homogeneous techniques are Electrophoretically Mediated Microanalysis, At-inlet and Transverse Diffusion of Laminar Flow Profiles. The main heterogeneous ones are Immobilized MicroEnzyme Reactors with enzymes grafted on either non-magnetic or magnetic particles. The overview covers the period from 2018 to early 2021. The applications range from drug discovery over natural products to food, beverage and pesticide analysis.

Investigation of viscoelastic focusing of particles and cells in a zigzag microchannel.

Microfluidic particle focusing has been a vital prerequisite step in sample preparation for downstream particle separation, counting, detection, or analysis, and has attracted broad applications in biomedical and chemical areas. Besides all the active and passive focusing methods in Newtonian fluids, particle focusing in viscoelastic fluids has been attracting increasing interest because of its advantages induced by intrinsic fluid property. However, to achieve a well-defined focusing position, there is a need to extend channel lengths when focusing micrometer-sized or sub-microsized particles, which would result in the size increase of the microfluidic devices. This work investigated the sheathless viscoelastic focusing of particles and cells in a zigzag microfluidic channel. Benefit from the zigzag structure of the channel, the channel length and the footprint of the device can be reduced without sacrificing the focusing performance. In this work, the viscoelastic focusing, including the focusing of 10μm polystyrene particles, 5μm polystyrene particles, 5μm magnetic particles, white blood cells (WBCs), red blood cells (RBCs), and cancer cells, were all demonstrated. Moreover, magnetophoretic separation of magnetic and nonmagnetic particles after viscoelastic pre-focusing was shown. This focusing technique has the potential to be used in a range of biomedical applications.

Magnetic intensification of mass transfer between fluidizing gas and Geldart-B nonmagnetizable particles: Property effects of added magnetizable particles

This work aimed to explore the property effects of added magnetizable particles on the magnetic intensification of mass transfer between the fluidizing gas and Geldart-B nonmagnetizable particles. A compromise volume fraction (xvM) of magnetizable particles in the resulting binary admixture was 0.40 to transmit the stabilizing effect of magnetic field to the nonmagnetizable particles and save the bed volume. When xvM was maintained the same (=0.40), the added magnetizable particles had an optimal size/density to maximize the magnetic intensification. When the gas velocity was three times the minimum fluidization velocity of the nonmagnetizable particles, the optimum size and density ratios between the added magnetizable particles and the nonmagnetizable particles were 0.41 and 2.99, respectively. When the mass fraction was kept constant (=0.77), the lighter magnetizable particles were preferred to transmit the magnetic stabilization. The property effects of added magnetizable particles on the magnetic intensification of mass transfer depended on its effects on the hydrodynamics in the resulting admixture MFB. Provided the added magnetizable particles could make the obtained admixture MFB locate in the magnetic stabilization flow regime, the mass transfer could be significantly intensified. The more stable the obtained magnetic stabilization, the better the magnetic intensification of the mass transfer.

Mass transfer intensification between fluidizing gas and Geldart‐B nonmagnetizable particles in magnetized fluidized bed

AbstractThis work aimed to intensify the mass transfer between fluidizing gas and Geldart‐B nonmagnetizable particles by simultaneously introducing magnetizable particles and applying the magnetic field. The mere addition of magnetizable particles hardly affected the interphase mass transfer. Moreover, such mass transfer was not improved by the subsequent application of the magnetic field under the magnetization‐LAST operation mode. However, the mass transfer was significantly enhanced by the magnetic field in the magnetic stabilization and transition flow regimes under the magnetization‐FIRST operation mode. Apparently, the mass transfer intensification depended not only on the magnetic field intensify (H) but also on the operation mode. The gas–solid contact performance in the magnetic stabilization flow regime was always comparable to that in fixed beds. Hence, further increases in H could not raise the magnitude of intensification but only increase the operating range and stability of the magnetic stabilization, which was in metastable equilibrium.

Influence of separation chamber shape in dry magnetic separator on the dispersion and separation of multiple magnetites

Dry magnetic separators are a common type of equipment for separating magnetic particles from nonmagnetic particles or relatively strong magnetic particles from relatively weak magnetic particles. However, the separation efficiency is not satisfactory when fine-grained particles are processed because of their strong tendency to aggregate. The separation efficiency of a dry magnetic separator depends on the optimization of the material characteristics and process variables, as well as the design characteristics of the equipment. However, previous studies on dry magnetic separators have neglected the influence of the separation chamber shape on the sorting efficiency. Therefore, in this study, three dry magnetic separators with separation chambers with different shapes are investigated, and a multiphysics coupling model is developed to simulate the separation process of fine magnetic particles in these three dry magnetic separators. The predicted results show that the wavy-shaped separation chamber (WSC) can promote the irregular movement of the airflow and then generate a large amount of vortex to promote the dispersion of particles. Moreover, the WSC can effectively improve the recovery of magnetite and high-grade intergrowth particles and the separation efficiency of the equipment. By comparing the experimental results with the simulation results, the correctness of the prediction results is verified. This study provides a new concept for improving the separation efficiency of fine multiple magnetites in dry magnetic separators.

Ferrofluidic Manipulator: Automatic Manipulation of Nonmagnetic Microparticles at the Air–Ferrofluid Interface

Manipulation of small-scale matter is a fundamental topic in micro and nanorobotics. Numerous magnetic robotic systems have been developed for the manipulation of microparticles in an ambient environment, liquid, as well as on the air-liquid interface. These systems move intrinsically magnetic or magnetically tagged objects by inducing a magnetic torque or force. However, most of the materials found in nature are nonmagnetic. Here, we report a ferrofluidic manipulator for automatic 2-D manipulation of nonmagnetic objects floating on top of a ferrofluid. The manipulation system employs 8-cm-scale solenoids, which can move nonmagnetic particles by deforming the air-ferrofluid interface. Using linear programming, we can control the motion of the nonmagnetic particles with a predefined trajectory of a line, square, and circle with a precision of 25.1 ± 19.5, 34.4 ± 28.4, and 33.4 ± 26.6 μm, respectively. The ferrofluidic manipulator is versatile with the materials and the shapes of the objects under manipulation. We have successfully manipulated particles made of polyethylene, polystyrene, a silicon chip, and poppy and sesame seeds. This article shows a promising venue for the manipulation of living and nonliving matter at the air-liquid interface.

Time-domain formulation of electromagnetic scattering based on a polarization-mode expansion and the principle of least action

An approach to the full wave analysis of the time evolution of the polarization induced in the electromagnetic scattering from dispersive nonmagnetic particles is presented. It is based on the combination of the Hopfield model for the polarization field, the expansion of the polarization field in terms of static longitudinal and transverse modes of the particle, the expansion of the radiation field in terms of transverse wave modes of free space, and the principle of least action. The polarization field is linearly coupled to the electromagnetic field. The losses of the matter are described thorough a linear coupling of the polarization field to a bath of harmonic oscillators with a continuous range of natural frequencies. The set of linear ordinary differential integral equations of convolution type of the overall system is reduced by eliminating both the radiation degrees of freedom and the bath degrees of freedom, and the reduced system of equations is studied. The role played by the radiation field in the coupling between the longitudinal and transverse mode amplitudes of the polarization is described. The principal characteristics of the temporal evolution of the mode amplitudes are found as the particle size varies, including the impulse response. Results are presented for the analytically solvable spherical particle. The proposed approach leads to a general method for the analysis of the temporal evolution of the polarization field induced in dispersive particles of any shape, as well as for the computation of transients and steady states.

Experimental Study of the Deposition of Magnetic Particles on the Walls of Microchannels.

This study analyzes experimentally the deposition of magnetic beads on the walls of a square microchannel by the action of a nearby cubical magnet. The deposition has been studied for different magnetic bead sizes, flow rates, magnetic conditions and with solutions of magnetic and non-magnetic particles. Images of the time evolution of the deposition under the different conditions have been analyzed to determine the spatial distribution of the accumulation and the growth rate of the depositions. It has been found that the way in which the magnetic beads are deposited on the walls of the microchannel depends strongly on their size and the magnetic configuration. The accumulation of the major part of particles is on the wall closest to the magnet and, depending on the size of the particles, near the magnet leading and trailing edges or near the center of the magnet. The experiments with magnetic and non-magnetic particles revealed the screening effect of the non-magnetic particles on the deposition. In this case, the non-magnetic particles displace the deposition toward the region near the center of the magnet and near the trailing edge.

Optimum Coil-System Layout for Magnet-Driven Superconducting Magnetic Density Separation

This article discusses the optimum layout of coils of a superconducting magnet system for magnetic density separation (MDS). MDS is a novel separation technology that combines a vertical magnetic field gradient with a ferrofluid to separate mixtures of non-magnetic particles based on their mass density. The MDS process can separate more than two types of particles in a single process step, thereby distinguishing it from other separation techniques using a ferrofluid. The authors are currently constructing a superconducting MDS demonstrator. Ideally, the gradient of the magnetic field magnitude should change only with the distance above the magnet but remain constant in a horizontal plane. In principle, such an ideal field profile can be generated with an infinite harmonic sheet current. In practice, edge effects appear due to the necessity of using a finite number of coils. These cause a horizontal component in the field gradient and also change the vertical component. We compare the vertical magnetic field gradient of various coil layouts to see which configuration performs best. To facilitate ease of production, the analysis is restricted to flat racetrack coils. The main result is that the specific shape of a racetrack coil has a larger influence on the vertical gradient than the number of coils. The feed particles need to be pushed through the separation chamber from the insertion to the collection point. One option to realize this is to use an MDS setup in which the magnet is inclined with respect to the horizontal plane. This tilting results in a horizontal magnetic force component, which drives feed particles through the fluid bed. We show that a three-coil layout provides the largest usable fluid bed depth for a wide range of tilt angles.

Determining minimum fluidization velocity in magnetized fluidized bed with Geldart-B particles

This work aimed to solve the controversies about defining and determining the minimum fluidization velocity (Umf) in the magnetized fluidized bed (MFB). It should be defined rigorously from the physics behind the secondary phenomena such as bed pressure drop and particle motion. Since Umf demarcates the transition from the fixed-bed to the fluidization flow regime, it could not be determined from the ΔPb–Ug↓ curve but could from the ΔPb–Ug↑ curve. Moreover, the initial fixed bed for measuring this curve must meet its definition. For the MFB with purely magnetizable particles, it could be obtained via decreasing Ug gradually from full fluidization to zero at H = 0 kA/m to minimize the wedging effect. For the MFB with magnetizable and nonmagnetizable particles, such a decrease of Ug should be quick to simultaneously minimize the wedging effect and segregation. The as-determined Umf remained invariant with H in both types of MFBs.

Operating range of magnetic stabilization flow regime for magnetized fluidized bed with Geldart-B magnetizable and nonmagnetizable particles

The magnetic stabilization flow regime could also be created for Geldart-B nonmagnetizable particles provided some magnetizable particles are introduced and the magnetic field is applied. This study aimed to explore the size (dpM) and density (ϿpM) effects of magnetizable particles on its operating range. The upper limit (UmbH) could not be determined from the οPb⿿Ug⿿ curve but could from analyzing the variation of οPb-fluctuation with increasing Ug. Due to the variation of UmfH (lower limit) with dpM and ϿpM, both UmbH⿿UmfH and (UmbH⿿UmfH)/UmfH were used to quantify the operating range of magnetic stabilization. UmbH⿿UmfH varied hardly with dpM but increased significantly with decreasing ϿpM. (UmbH⿿UmfH)/UmfH increased as dpM or ϿpM decreased. It was more difficult for the nonmagnetizable particles to escape from the network formed by the smaller/lighter magnetizable particles. For the same magnitude of change, dpM had a stronger effect than ϿpM on (UmbH⿿UmfH)/UmfH. Neither UmbH⿿UmfH nor (UmbH⿿UmfH)/UmfH varied monotonously with the minimum fluidization velocity of the magnetizable particles, indicating that no straightforward criterion for matching the magnetizable particles to the given nonmagnetizable particles could be established based on their minimum fluidization velocities to maximize the operating range of magnetic stabilization.

Segregation in magnetized fluidized bed with Geldart-B magnetizable and nonmagnetizable particles

For magnetized fluidized beds with Geldart-B magnetizable and nonmagnetizable particles operated under the magnetization-LAST mode, segregation occurs and deepens as the magnetic field intensity increases. This work aimed to explore the effects of particle size and density difference on such segregation. The field intensities (His and Hcs) for the segregation to initiate and complete increased as the gas velocity (Ug) increased. Moreover, their increases were steeper at higher gas velocities. The increase of Ug raised not only the collision to the magnetic chains but also their mixing tendency with the nonmagnetizable particles. For the given nonmagnetizable particles and Ug, His and Hcs increased as the size or density of the magnetizable particles decreased, indicating that it was more difficult for the segregation to occur and complete. Additionally, the smaller/lighter the magnetizable particles, the steeper the variations of His and Hcs with Ug. A much stronger magnetic field was required for more of such magnetizable particles to form the desired magnetic chains and keep the desired size. Segregation could only be postponed but completely prevented under the magnetization-LAST operation mode however the two types of particles were matched.

PENENTUAN NILAI SUSEPTIBILITAS DAN UKURAN PARTIKEL MAGNETIK PASIR ALAM LOGAS KABUPATEN KUANTAN SINGINGI MENGGUNAKAN VARIASI UKURAN BALL MILLING

Magnetic properties and morphology of natural sand has been carried out in Logas Village, Kuantan Singingi Regency have been determined. Iron sand samples were processed using iron sand separator (ISS) prior to ball milling for separating between magnetic and non magnetic particles. The product of ISS was milled for 90 hours using ball milling first step method with milling ball size of 1.5 cm. Themagnetic and non-magnetic particles of ball milling products were separated using Neodymium Iron Boron (NdFeB) magnet. The product of ball milling first step then was milled for another 30 hours with milling ball size of 0.5 cm and 0.7 cm. The susceptibility and mass susceptibility were determined based on magnetic induction of a selenoid measured using Probe Magnetic Pasco PS-2162. The composition of Logas natural sand was measured using x-ray fluorescence spectroscopy (XRF). The morphology of the magnetic particles are determined using scanning electron microscope (SEM). The results showed that the particle size of natural sand for 90 hours + 30 hours milling displays the particle sizes from 100 µm to 800 µm. As for the particle size of the samples synthesized with 90 hours + 30 hours for 0.7 cm milling ball size, the particles are almost evenly distributed, which is about 5 µm to 100 µm. The content of Fe and Ti in the sample has increased while for Si has decreased. Mass susceptibility increases with increasing ball milling time and ball milling size.

Agglomerate processing and recycling options in magnetic seeded filtration

In magnetic seeded filtration, a hetero-agglomeration between non-magnetic target and magnetic seed particles is induced and the agglomerates are subsequently removed by magnetic separation. The necessary addition of magnetic material constitutes the main criticism of the process. In this study, three different agglomerate processing and seed particle recycling strategies were tested experimentally: Thermal breakup, in which the non-magnetic fraction is decomposed at elevated temperatures, chemical breakup, where non-magnetic particles are dissolved in a solvent and lastly mechanical breakup, in which agglomerates are broken under stress. All approaches were investigated in a cyclical manner to disclose eventual long-term effects. Generally, all approaches showed high recycling rates of magnetic seed particles resulting in consistently high separation efficiencies throughout the experimental cycles. Where applicable, the non-magnetic fraction was also recovered at high rates. This work proofs general feasibility of all three recycling approaches, while also discussing the respective benefits, limitations and possible applications.